The present invention relates to polishing pads. In particular, the polishing pads of the present invention are porous and composed of particulate polymer, e.g., particulate crosslinked polymer, and crosslinked organic polymer binder that binds the particulate polymer together. Polishing pads according to the present invention are useful for polishing articles, e.g., the chemical mechanical polishing or planarization of semiconductor substrates.
The polishing or planarization of the rough surface of an article, e.g., a semiconductor substrate, to a smooth surface generally involves rubbing the rough surface with the work surface of a polishing pad using a controlled and repetitive motion. Typically, a polishing fluid is interposed between the rough surface of the article that is to be polished and the work surface of the polishing pad. The polishing fluid may optionally contain an abrasive material, e.g., particulate cerium oxide.
The fabrication of semiconductor wafers typically involves the formation of a plurality of integrated circuits on a semiconductor substrate of, for example, silicon or gallium arsenide. The integrated circuits are generally formed by means of a series of process steps in which patterned layers of materials, such as conductive, insulating and semiconducting materials, are formed on the substrate. In order to maximize the density of integrated circuits per wafer, it is necessary to have an extremely planar precision polished substrate at various stages throughout the semiconductor wafer production process. As such, semiconductor wafer production typically involves at least one, and more typically a plurality of polishing steps, which involve the use of one or more polishing pads.
The polishing steps typically involve rotating the polishing pad and/or semiconductor wafer substrate against each other in the presence of a polishing fluid. The polishing fluid is often mildly alkaline and may optionally contain abrasive particulate materials, e.g., silica. The pad acts to mechanically polish the semiconductor substrate, while the polishing fluid serves to chemically polish the substrate and to facilitate the removal and transport of abraded material off of and away from the rough surface of the article.
The pressure at which the polishing pad and substrate are pressed against each other, and the rate at which they are turned against each other is generally maintained within high tolerances to ensure a controlled rate of substrate removal. Unfortunately, polishing and planarization characteristics are often variable from pad-to-pad, and throughout the operating lifetime of a given pad (i.e., intrapad variability). Correspondingly, variations in the polishing characteristics of the pads typically results in inadequately polished and planarized substrates, which may have to be scrapped. Physical properties of polishing pads that can result in variable polishing characteristics include, for example, variations in pore volume and pore size from one pad to the next, and within a single pad.
It is desirable to develop polishing pads that exhibit reduced and preferably minimal pad-to-pad variation in polishing and planarization characteristics. It is further desirable to develop polishing pads that exhibit reduced and preferably minimal variations in polishing and planarization characteristics throughout the operating lifetime of the pad.
International Publication No. WO 98/47662, published under the Patent Cooperation Treaty, describes a polishing pad for semiconductor substrates, which is fabricated from sintered particles of thermoplastic resin. The polishing pads of International Publication No. WO 98/47662 are further described as being porous and uniform.
International Publication No. WO 96/15887, published under the Patent Cooperation Treaty, describes polishing pads prepared by pressure sintering powder compacts of thermoplastic polymer at temperatures above the glass transition temperature but not exceeding the melting point of the thermoplastic polymer. The polishing pads of International Publication No. WO 96/15887 are further described as having interconnected porosity, which is uniform in all directions.
U.S. Pat. Nos. 5,900,164 and 5,578,362 describe polymeric polishing pads, which include a polymeric matrix impregnated with a plurality of polymeric microelements, wherein each polymeric microelement has a void space therein. The ""164 and ""362 patents further describe the polymeric microelements at the work surface of the polishing pad as becoming softer than those microelements embedded in the subsurface of the pad, when the work surface is in contact with a working environment.
In accordance with the present invention, there is provided a polishing pad comprising:
(a) particulate polymer selected from particulate thermoplastic polymer, particulate crosslinked polymer and mixtures thereof; and
(b) crosslinked organic polymer binder, which binds said particulate polymer together,
wherein said particulate polymer and said crosslinked organic polymer binder are distributed substantially uniformly throughout said pad, and said pad has a percent pore volume of from 2 percent by volume to 50 percent by volume, based on the total volume of said polishing pad (e.g., from 5 percent by volume to 40 percent by volume, or from 10 percent by volume to 30 percent by volume, based on the total volume of the polishing pad). The percent pore volume of the polishing pad is calculated using the following equation,
100xc3x97(density of the pad)xc3x97(pore volume of the pad)
wherein the density is determined in accordance with American Standard Test Method (ASTM) No. D 1622-88, and the pore volume is determined by means of the art-recognized mercury porosimitry method, as describe further herein in the Examples.
The features that characterize the present invention are pointed out with particularity in the claims, which are annexed to and form a part of this disclosure. These and other features of the invention, its operating advantages and the specific objects obtained by its use will be more fully understood from the following detailed description and the accompanying drawings in which embodiments of the invention are illustrated and described.
Other than in the operating examples, or where otherwise indicated, all numbers or expressions, such as those expressing structural dimensions, pressures, flow rates, etc, used in the specification and claims are to be understood as modified in all instances by the term xe2x80x9cabout.xe2x80x9d